Locating devices have been used for a long time to detect objects—such as electrical cables, water lines, pipes, metallic framework or wooden beams—enclosed in a medium, e.g., in a wall, ceiling, or floor. These devices include inductive devices, i.e., devices that produce a magnetic field that is disturbed by the metallic objects enclosed in a medium. In addition to these inductive devices, capacitive devices, mains voltage detectors, and high-frequency detectors are also used. With mains voltage detectors or AC detectors, only a receiving conductor loop system is used to detect the desired signal and, therefore, to locate an object.
A problem associated with these devices in particular is the enormous dynamics of the sensors used that exists even though the measuring device has been calibrated; this results in a variation of the signal intensity of the measurement signal that is detected. In order to detect as many metallic objects of different sizes and embedded depth—i.e., the distance of the enclosed object from the measuring device—as possible using metal-locating devices, a large dynamic range must be covered. The large dynamic range of the measurement signal from sensors of this type results from the depth of the objects to be measured in the enclosing medium, and from the characteristic properties of the particular material to be detected. For example, the sensor signal or measurement signal generated by a copper cable located deep inside a wall is smaller—by several magnitudes—than that produced by an iron pipe located 2 cm inside the wall.
With many of the known locating devices, particularly metal-locating devices or mains-voltage locating devices, it is therefore often possible to manually adjust the sensitivity of the sensor, i.e., for the user to manually adjust the sensitivity of the sensor. Rotary potentiometers, e.g., with an associated rotating wheel installed on the housing of the locating device, are used for this purpose.
With other locating devices, the sensitivity of the sensor and, therefore, the intensity of the detected measurement signal, can be regulated by recalibrating the device for the objects that are present.
With devices of this type, however, it is difficult to detect and/or exactly locate objects of different sizes, e.g., copper cables and steel beams, with one device setting. If the signal intensity of the detected measurement signal is too great, for example, this results in overdrive of the receiving amplifier of a sensor of this type. It is so critical because, in this case, it is no longer possible to detect an increase or decrease in a signal over a wide range, although this must be done in order to locate an enclosed object exactly. In a case such as this, an enclosed object causes maximum deflection of the measuring device over a broad lateral range, so that the user is still uncertain as to the exact position of the object. Nor is it possible, e.g., to detect objects that are located close to each other as two separate objects.
Several proposed designs for detecting signals with large dynamics are known in the related art.
It is possible, e.g., to design the display of the measuring device such that the entire dynamic range is depicted. This is realizable, e.g., by using a logarithmic scale for the display size, which is correlated with the measurement signal. The disadvantage of a depiction of this type, however, is the fact that weak and very strong objects appear at the beginning and the end of the dynamic range of the displayed scale and are therefore very difficult to identify or locate, since the changes displayed in the display of the measuring device are relative small due to the scale that is used.
Publication DE 42 00 518 A1 makes known a metal detector with which metal hidden in a wall can be located and its depth determined using a sensor provided with two coil pairs. The two coil pairs of the sensor described in DE 4200518 A1 are each connected with an oscillator, and they oscillate continually at different frequencies. The signals, which are influenced by the metal, are measured and weighted for the evaluation. An intensity display on the measuring device characterizes the position of the metal for a user. To measure the depth of the hidden metal, i.e., to determine the depth of the enclosed object relative to the surface of a wall, a floor, or the like, a boosting device on the measuring device is actuated once the metal is located in order to boost the metal detector by a defined amount. The depth of the hidden metal is calculated by performing a second measurement and taking into consideration the predefined changed distance from the wall surface. A manually operated marking device makes it possible to characterize the location of the measurement and the enclosed object.